Water filter glossary — plain-language definitions for Australian buyers

The most common water filter media. Removes chlorine, taste, odour, and some chemicals via adsorption — contaminants stick to the porous surface. Granular Activated Carbon (GAC) has higher flow rates but shorter contact time. Carbon Block is denser and more effective, especially for chloramine reduction. Neither removes hardness, fluoride, nitrates, or dissolved metals without additional stages.

The process by which contaminants bind to the surface of a filter medium (typically activated carbon). Different from absorption (where material is taken into a substance). Adsorption is the primary mechanism in carbon filters — when the surface sites are full, the filter is exhausted.

The national framework for drinking water quality in Australia, published by NHMRC and managed by NHMRC/NRMMC. Sets both health-based guidelines (safety limits) and aesthetic guidelines (taste, odour, appearance). Compliance is managed by state water utilities. The ADWG is the standard all Australian town water must meet. Updated June 2025 to include lower PFAS limits.

A measure of water's capacity to neutralise acids — primarily from bicarbonate, carbonate, and hydroxide ions. High alkalinity buffers pH changes. Low alkalinity (e.g. rainwater) makes water more corrosive. Relevant for understanding copper pipe corrosion (blue-green staining) and for TAC system effectiveness.

A naturally occurring heavy metal found at elevated levels in some Australian groundwater, particularly in WA Goldfields, outback SA, and parts of NT. The ADWG health guideline is 10 µg/L. RO (NSF 58) achieves 93–96% arsenic removal. Relevant primarily for bore water users in affected regions.

Single-celled microorganisms. In drinking water, the primary indicator organisms are E. coli and total coliforms. Australian town water is treated to achieve 'not detected' for E. coli per 100 mL. Carbon filters do not reliably remove bacteria. Ceramic filters (0.2 micron), UV treatment, and boiling are effective.

A maintenance process for some whole-home and commercial filter systems where water flow is reversed through the media to flush out trapped sediment and rebed the media. Required periodically for sand filters, multi-media filters, and some TAC/softener systems. Not all systems require backwashing.

A 20" × 4.5" filter housing format used in whole-home and high-flow applications. Larger cartridge volume means longer cartridge life and better flow rates than standard 10" housings. Standard in Australian point-of-entry (whole-home) filter installations. Compare with standard 10" × 2.5" housings used in under-sink systems.

Groundwater accessed through a drilled bore or well. Quality varies enormously by location — from near-drinking-water quality to highly mineralised, iron-rich, or bacterially contaminated. Should always be tested before use. Not regulated by state water utilities. Common in rural WA, SA, QLD. Typically requires dedicated treatment based on test results.

The primary compound responsible for water hardness and scale. Dissolved calcium and bicarbonate ions precipitate as solid calcium carbonate (limescale) when water is heated or evaporated. Hardness is expressed in mg/L CaCO₃. TAC systems change the crystal structure of CaCO₃ to prevent scale formation without removing it from the water.

A solid block of compressed activated carbon with a defined pore structure. Provides more consistent contact time than GAC, better chloramine reduction, and more effective lead and cyst removal when NSF 53 certified. The standard recommendation for whole-home and under-sink filter stages. Available in 0.5, 1, 5, and 10 micron ratings.

An enhanced form of activated carbon with a modified surface chemistry that facilitates oxidation-reduction reactions. More effective than standard GAC or carbon block at removing chloramine (monochloramine) and hydrogen sulfide. Used in whole-home systems for chloramine cities (Sydney, Brisbane, Adelaide, GWW Melbourne). Should specify 'catalytic carbon' or 'chloramine reduction' — standard carbon is insufficient.

A filter element made from diatomaceous earth, ceramic, or similar material with a pore size of 0.2–0.5 microns. Removes bacteria, protozoa (Giardia, Cryptosporidium), and sediment by mechanical filtration. Does not remove viruses, dissolved chemicals, or chlorine without an activated carbon core. Used in gravity filter systems (Berkey-type) and some under-sink units.

A disinfectant formed by combining chlorine and ammonia. Used in most large Australian water distribution systems (Sydney, Brisbane, Adelaide, GWW Melbourne) because it persists over longer pipe distances than free chlorine without breaking down. Harder to remove than free chlorine — requires catalytic carbon or Vitamin C. NSF 177 (shower filter standard) tests free chlorine only, not chloramine.

The primary disinfectant in most small to medium Australian water supplies and in Perth and Melbourne YVW/SEW east/south zones. More reactive and easier to remove than chloramine. Standard activated carbon (GAC or block) removes free chlorine effectively. Volatilises rapidly at shower temperatures. ADWG aesthetic guideline: 0.6 mg/L (taste threshold).

A protozoan parasite that causes cryptosporidiosis — persistent gastrointestinal illness. Found in surface water including creeks, rivers, and dams. Resistant to chlorine at normal treatment doses. Removed by ceramic filtration (0.2–1 micron), hollow fibre membranes, and UV treatment. Not removed by standard carbon filters.

Compounds formed when chlorine or chloramine reacts with organic matter in source water. Trihalomethanes (THMs) and haloacetic acids (HAAs) are the main categories. The ADWG sets health guidelines for total THMs (250 µg/L). Carbon block filtration reduces THMs. Associated in some epidemiological studies with adverse reproductive outcomes at high chronic exposure.

Added to Australian capital city water at 0.56–1.0 mg/L for dental health benefits. Sydney has the highest target (1.0 mg/L). The ADWG health guideline is 1.5 mg/L. Standard carbon filters have essentially no effect on fluoride. Only RO (removes 95–96%) and activated alumina (removes 55–70%) reduce fluoride meaningfully. Boiling concentrates fluoride.

The volume of water a filter system processes per unit time, typically expressed in litres per minute (L/min). Whole-home systems need to match the peak flow demand of the household (typically 25–50 L/min for a family home). Under-sink systems operate at lower flow rates (2–6 L/min). RO systems are slowest (0.1–0.5 L/min at the membrane).

A cosmetic condition causing white spots or streaking on permanent teeth, caused by excess fluoride during tooth development. Associated with prolonged infant formula preparation using water at the higher end of Australian fluoride targets (particularly Sydney at 1.0 mg/L). Not a health emergency — primarily cosmetic. Prevented by using RO water for infant formula if a concern.

Loose activated carbon granules used as a filter medium. Higher flow rates than carbon block but lower contaminant contact time. Effective for taste, odour, and free chlorine. Less effective than carbon block for chloramine. Can harbour bacteria in warm, wet conditions (important for shower filters). Standard media in many entry-level whole-home and pitcher filters.

A protozoan parasite causing giardiasis — persistent gastrointestinal illness. Found in Australian surface water. Resistant to chlorine. Removed by ceramic filtration, hollow fibre membranes, and UV treatment. Not removed by standard carbon filters. Particularly relevant for caravan, camping, and rural water users.

A measure of dissolved calcium and magnesium in water, expressed in mg/L CaCO₃ or mg/L. Causes scale (limescale) on heated surfaces, appliances, and pipes. Reduces soap lather. Does not pose a health risk at levels found in Australian water. Classification: soft 0–60, moderate 60–120, hard 120–180, very hard 180+ mg/L. Perth northern outer zones reach 200–350 mg/L.

A water treatment process where ions in the water are exchanged for ions on a resin bead. In salt-based water softeners: calcium and magnesium (hardness) ions are exchanged for sodium ions. In deionisation systems: all ions are removed. Ion exchange is the mechanism in all salt-based softeners and some RO post-treatment stages.

Dissolved iron causes orange-brown staining on tapware, laundry, and fittings. Common in bore water and some groundwater-dominant Perth zones. ADWG aesthetic guideline: 0.3 mg/L. Above 0.3 mg/L causes visible staining. Removed by oxidation + filtration, catalytic carbon, or RO. Iron at elevated levels can foul RO membranes if not pre-treated.

A copper-zinc alloy media that uses electrochemical redox reactions to remove free chlorine, some heavy metals, and inhibit bacteria growth. The basis of most NSF 177-certified shower filters. Does not address chloramine. Does not remove hardness, fluoride, or PFAS. Effective at shower temperatures unlike activated carbon.

A toxic heavy metal with no safe exposure level for infants and children. Does not occur naturally in Australian mains supply water at concerning levels — the risk is from household plumbing (lead-based solder used in pre-1980s copper pipe joints). Removed by NSF 53-certified carbon block (verified claim required) and RO (NSF 58). Boiling concentrates lead.

A naturally occurring metal. In elevated concentrations (above 0.1 mg/L ADWG aesthetic) causes black or dark brown staining and metallic taste. Found alongside iron in bore and groundwater. Can cause neurological effects at very high chronic exposure. Removed by oxidation + filtration or RO.

The semipermeable membrane at the core of a reverse osmosis system. Typically made from thin-film composite (TFC) polyamide. Pore size approximately 0.0001 microns — small enough to reject dissolved salts, metals, PFAS, nitrates, fluoride, and most dissolved contaminants. Must be replaced every 2–5 years depending on water quality and usage. Requires pre-filtration to protect from fouling.

A unit of measurement equal to one millionth of a metre. Used to describe filter pore size. Reference points: human hair ≈70–100 microns; Giardia ≈8–15 microns; Cryptosporidium ≈4–6 microns; bacteria ≈0.5–5 microns; viruses ≈0.02–0.3 microns. A 0.2-micron ceramic filter removes bacteria and protozoa; RO membranes at 0.0001 microns remove viruses and dissolved ions.

Plastic particles under 5mm in size. Found in Australian tap water, bottled water, and the environment. The health significance of microplastics in drinking water is under active research — IARC classified PFAS (a different chemical) separately. RO membranes and 0.5-micron or finer filters remove microplastics from water. Standard carbon filters may reduce but not eliminate them.

Australia's peak body for laboratory accreditation. NATA-accredited laboratories meet rigorous quality management standards. For drinking water testing, always use a NATA-accredited lab — results are defensible, comparable to ADWG guidelines, and reliable. Search at nata.com.au.

Dissolved nitrogen compounds from agricultural runoff, septic systems, and natural decomposition. The ADWG health guideline is 50 mg/L. Above this level, dangerous for infants under 3 months (blue baby syndrome/methemoglobinemia). Metropolitan mains water is typically below 5 mg/L. Bore and rural water near agriculture may exceed guidelines. Removed by RO (87–90%). Boiling concentrates nitrates.

An independent US-based organisation that develops standards and certifies water treatment products. NSF certification is the primary independent standard for water filter claims in Australia. Verification at nsf.org is free. Key standards: NSF 42 (taste/aesthetic), NSF 44 (softener capacity), NSF 53 (health contaminants including lead), NSF 55 (UV systems), NSF 58 (RO), NSF 177 (shower filters).

The NSF standard for aesthetic effects — taste, odour, and chlorine/chloramine reduction. Does not verify removal of health contaminants like lead, PFAS, or nitrates. Most basic carbon filters carry NSF 42. For chloramine-specific claims, look for NSF 42 with a specific chloramine claim tested.

The NSF standard for health effects — lead, cysts (Cryptosporidium, Giardia), VOCs, and certain heavy metals. A filter must list the specific contaminant and reduction percentage on its NSF 53 certificate. "NSF 53 certified" without a specific lead claim does not mean lead is removed. Verify at nsf.org.

The NSF standard for reverse osmosis systems. Covers TDS reduction, lead, fluoride, nitrates, PFAS, and other dissolved contaminants. The standard for verifying RO system performance. NSF 58 certification confirms the membrane and pre/post filters have been tested as a complete system.

The only NSF standard specifically for shower filters. Tests for free chlorine reduction only — a single requirement of 50% minimum reduction for a defined volume. Does not test chloramine, lead, heavy metals, PFAS, or bacteria. A shower filter with NSF 177 certification has not been verified for chloramine removal.

"Forever chemicals" — a class of synthetic compounds resistant to environmental degradation. PFAS contamination in Australian drinking water has been identified near RAAF bases (Williamtown, Oakey, Tindal, Edinburgh), certain airports, and industrial sites. The ADWG was updated June 2025 to substantially lower PFAS guideline values. RO (NSF 58) removes 90–96% of PFAS. Activated carbon (GAC) provides partial removal at high contact times.

A measure of hydrogen ion concentration — the acidity or alkalinity of water. pH 7.0 is neutral. Below 7.0 is acidic (corrosive to metals). Above 7.0 is alkaline. The ADWG aesthetic guideline range is 6.5–8.5. Australian city tap water is typically 7.2–8.0. Rainwater is naturally low pH (5.5–6.5) and more corrosive to copper plumbing.

A water treatment system installed at the main water supply inlet, treating all water entering the property. Whole-home filters, TAC systems, and salt-based softeners are POE systems. Contrasts with Point of Use (POU) systems which treat water at a single tap.

A water treatment system installed at a specific tap or outlet — treating water for drinking and cooking only. Under-sink RO systems, benchtop filters, and tap-mount filters are POU systems. More affordable than POE systems but do not protect appliances or shower water.

The reduction in water pressure caused by passing water through a filter. All filters reduce pressure to some degree. Filters that are clogged or near end-of-life cause greater pressure drop. Excessive pressure drop is a sign the cartridge needs replacing. Big Blue housings cause less pressure drop than standard 10" housings at the same flow rate.

A filtration technology that uses pressure to push water through a semipermeable membrane with 0.0001-micron pore size, rejecting dissolved salts, metals, fluoride, nitrates, PFAS, chloramine, and virtually all dissolved contaminants. TDS reduction typically 85–96%. Produces waste water (2:1 to 5:1 ratio of waste to product water). The NSF 58 standard applies. Not suitable for producing very large volumes due to slow production rate.

The white, chalky mineral deposit formed when hard water is heated or evaporated. Primarily calcium carbonate. Accumulates on heating elements, shower heads, tap aerators, heat exchangers, and inside kettles. Insulates heating elements — each 6mm of scale increases energy consumption by approximately 10% (Battelle study). Prevented by TAC or softener systems. Not a health risk.

A filter that removes physical particles — sand, rust, silt, fine debris — from water. Typically a pleated or wound polypropylene cartridge rated in microns (5, 10, 20, or 50 micron). Used as a first stage in multi-stage systems to protect carbon and RO stages from premature fouling. Replace when visibly brown or when flow rate drops.

A salt-free water conditioning technology that changes the crystal structure of calcium carbonate so it remains suspended in water rather than depositing as hard scale on surfaces. Does not remove calcium or magnesium — the water chemistry is unchanged. No salt, no backwashing, no sodium addition, no waste water. Media lasts 3–5 years. Appropriate for hardness 60–200 mg/L. For very hard water above 200 mg/L, a salt-based softener may be more effective.

The combined concentration of all dissolved ions in water, measured in mg/L or ppm by electrical conductivity. A TDS meter measures conductivity and estimates TDS from it. The ADWG has no health-based guideline for TDS — the 600 mg/L figure is an aesthetic (taste) guideline only. High TDS from calcium and magnesium is not a health concern. TDS meters cannot distinguish between safe minerals and harmful contaminants.

A handheld device that measures electrical conductivity and converts it to an estimated Total Dissolved Solids reading. Cost: $15–$30. Useful for: verifying RO membrane performance (should show 85–95% reduction), detecting sudden supply changes, initial bore water screening. Cannot detect chloramine, lead, bacteria, PFAS, nitrates, or specific contaminants at typical concentrations. Frequently used in onsite water filter sales demonstrations to create alarm about normal mains water readings.

A point-of-use filter system installed in the cabinet under the kitchen sink, plumbed to a dedicated filtered water tap or to the existing cold water tap. Provides higher flow rates and larger cartridge capacity than benchtop or pitcher filters. Available in single-stage (taste), multi-stage (health contaminants), and RO configurations. Requires a plumber for installation. Most effective and practical approach for drinking and cooking water filtration.

Ultraviolet light at 254nm wavelength inactivates bacteria, viruses, and protozoa by damaging their DNA. Does not remove chemical contaminants, sediment, or dissolved minerals. Requires clear water — turbid water blocks UV penetration. NSF 55 Class A applies to systems for treating unknown or potentially contaminated water (254 mJ/cm² minimum dose). UV lamps must be replaced annually. Used in bore water treatment systems and as a final stage in caravan/camping filtration.

A shower filter medium that chemically neutralises both free chlorine and chloramine through a fast reduction reaction. The only shower filter medium with documented effectiveness against chloramine. Used by the San Francisco PUC for chloramine network guidance. Cartridges dissolve in 4–8 weeks and require frequent replacement. Recommended for chloramine cities (Sydney, Brisbane, GWW Melbourne, Adelaide) where KDF and standard carbon are ineffective.

Organic chemicals that vaporise at room temperature. In water, relevant VOCs include pesticides, industrial solvents, and some disinfection by-products. NSF 53 certified carbon filters reduce many VOCs. RO provides comprehensive VOC removal. Metro mains water VOC concentrations are typically very low.

An ion exchange system that genuinely removes calcium and magnesium from water, replacing them with sodium ions. Produces 'soft' water that lathers better and prevents scale. Ongoing cost: salt purchase and periodic backwashing. Adds sodium to water — relevant for CKD and hypertension patients. Most effective for very hard water (above 200 mg/L). Contrasts with TAC systems which prevent scale without removing minerals.

Australian mandatory certification for plumbing products that contact drinking water — including filter housings, fittings, and taps. Managed by the Australian Building Codes Board (ABCB). Products must carry the WaterMark symbol with a licence number. Verify at watermark.org.au. Always require WaterMark-certified fittings for any whole-home or under-sink installation.